Obtaining bottles or containers by blowing special preforms appropriately heated inside a mould of the desired shape is a method widely used in the packaging field, in particular for making bottles or containers.
Two basic methods exist: simple blowing and stretch-blow moulding, the latter of which provides for pneumatic blowing and contemporary mechanical stretching of the preform in the mould. In both cases the preforms must reach the blowing or stretch-blow moulding machine in a thermal condition corresponding to the softening point of the material, so they may be plastically deformed inside the moulds.
The production of such bottles usually requires a high hourly production rate so as to reduce the moulding costs of each bottle or container to a minimum, since increased costs would significantly influence the final cost of the product.
Much effort has therefore been made to automate and speed up production methods.
Machines for blowing or stretch blow moulding preforms are known and typically include a plurality of moulds which can be opened, including two half-moulds hinged at one end and actuated by means of levers appropriately positioned and sized to allow the opening and closing thereof in a synchronised manner with predefined loading phases of the preforms and unloading phases of the moulded bottle. Such levers are generally actuated by means of a shaped cam coupling, such coupling being suitable for providing reciprocated movement with progress defined by the shape of the cam.
More specifically, such coupling includes a suitably shaped so-called “cam” profile and a sliding so-called “driven” element, forced to slide along such profile and able to provide mechanical utility with movement depending on the shape of the profile.
Often, to achieve a production high rate, a plurality of moulds are positioned radially around a central rotation axis on a rotating blowing machine, wherein the means for opening and closing the moulds are synchronised with the movement of other devices which co-operate in the functioning of the machine such as a device for moving the incoming preforms and the outgoing bottles, or a blowing device for moving various components of the moulds.
This way some of the processing steps on each successive bottle according to the rotation of the machine, are performed during other processing steps on the previous bottle.
Generally, the aforesaid mechanical devices are actuated singly by separate cams, shaped on the basis of the sequence or the duration of the required movements. In particular, various devices of a mould present their respective driven elements that are projected and orientated so that in a predefined portion of the rotation of the machine they are channelled into respective guides or cams, shaped in a manner suitable for imparting predefined movements on the driven element, which coordinates such movements to the various devices in a predefined manner.
In particular, in previously existing rotary machines having a plurality of moulds, each mould includes two half-shells hinged around a hinge axis parallel to the rotation axis of the machine, which can be closed or opened in a synchronised manner by means of an actuating device actuated by a cam coupling.
In such machines, the half-shells have an end aperture, positioned in a direction parallel to the hinge axis, corresponding to a bottom portion of the bottle to be obtained. Such aperture is suitable for being alternatively closed and opened by a bottom suitable for being moved in a direction substantially perpendicular to the bottom of the bottle. The bottom supports a portion of mould suitable for permitting the moulding of the bottom of the bottle, which presents projections and recesses which extend in a direction substantially perpendicular to the bottom.
In such machines the bottom is moved by means of a mechanism which receives the motion from a respective driven element associated with a cam different from that actuating the opening and closing of the mould.
Such pre-existing moulds have the disadvantage that during the blowing of the preform the pressure of the fluid, generally air, inside the preform and therefore inside the mould, exerts an opening force thereon, which tends to open and misalign the edges of the half-shells resulting in the production of an imperfect bottle where the separation line between the two half shells remains clearly visible.
In an attempt to overcome this problem, certain moulds use a bolt suitable for being inserted so as to slide in peripheral passages made at one end of the mould opposite the hinge axis, which, when the mould is closed, is aligned with the other end enabling the bolt to be inserted in the passages which keeps the mould in a closed configuration during blowing. Such bolt must therefore be inserted in the passages before blowing to keep the half-shells closed and removed after blowing to enable the subsequent opening thereof. Such bolts are actuated automatically by means of a respective driven element which engages on a cam different from that performing the opening and closing of the gripper.
While resolving the problem of keeping the half-shells closed, the presence of the bolt entails the further disadvantage of slowing down the production chain in that it can only be inserted when the mould is fully closed. Thus, it is not possible to insert it during the opening and closing movement of the mould.
In addition, the presence of the bolt entails the disadvantage of having to use an additional cam and a corresponding expenditure of mechanical energy.
Such known machines also require extreme precision in the sizing and assembly of the separate cams, in positioning them in the correct relative position with each other to provide the correct mechanical synchronisation of the various mechanical devices actuated in the machine and in particular of the gripper and bottom, as well as the insertion of the bolt. When the various cams are not fitted with extreme positioning, precision forcing could occur between the various mechanical parts which would cause rapid wear of the mechanical couplings. Moreover, because of high functioning speeds, in extreme cases mechanical interferences or impact could occur resulting in damage to the machine.
For these reasons, such known machines do not allow maximum production rate to be exceeded.